Optical waveguides are often employed in integrated optical circuits or used as a transmission medium in optical communication systems to provide coupling from one mode in an optical waveguide to another mode, or from one waveguide to another. Optical fiber is one type of optical waveguide typically composed of a circular cross-section dielectric waveguide consisting of a dielectric material and covered by a second dielectric material with a lower refractive index. Optical fibers are most commonly made from silica glass, but can be also made from other materials such as plastic.
In Si Photonics, current 2D polarization beam splitter (PBS) and polarization beam combiner (PBC) have relatively large insertion loss and low polarization extinction ratio. Insertion loss is the ratio of output to input light power of a certain wavelength. While some approaches use lensed fibers to enhance coupling efficiency, this approach tends to require complex and sensitive sub-micron alignment.
Furthermore, photonic integrated circuits are typically polarization dependent. Because the state of polarization of light is not always constant for a single mode fiber, photonic integrated circuits may need to operate independent of polarization of the light communicated from the fiber.